This application is based on and claims priority from Japanese Patent Application No. 2007-223191, filed on Aug. 29, 2007, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection control apparatus, and, in particular, to a fuel injection control apparatus that is used to control a fuel injection unit such as an injector that is provided in a four-stroke engine serving as an internal combustion engine.
2. Description of Related Art
Conventionally, techniques are known that perform fuel injection during startup based on crank sensor signals, generator output voltage, and engine speed as the conditions for performing the initial fuel injection when starting (i.e., cranking) an internal combustion engine. These techniques are disclosed in (1) to (3) (see below).    (1) A technique is disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-3887 in which startup fuel injection is performed in accordance with a single pulse signal while the crank is being rotated, voltage change characteristics are then determined, and thereafter fuel injection is performed based on the results of this determination.    (2) A technique is disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-162691 in which, after an engine startup operation has begun, the initial fuel injection is performed when the output voltage from the generator reaches a set value.    (3) A technique is disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-162543 in which fuel injection is performed when the crank angle velocity at the intake top dead center reaches a reference angular velocity after cranking has commenced.
Among internal combustion engines that are started by manual cranking, in a case of displacement volume and high compression ratio internal combustion engine, some types of internal combustion engines exist that are only able to be cranked approximately three revolutions in a single startup operation.
In these types of engine, in order to ensure superior startability by obtaining a predetermined engine speed at the compression top dead center where ignition takes place, it is common for an operation to discover the startup commencement crank angle to be performed.
There is a problem in that, fuel injection is performed during this operation to detect the startup commencement crank angle, excessive fuel is taken into the intake pipe and combustion chamber, and, as a results, startability during the actual startup operation is deteriorated.
In the technique disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-3887, because fuel injection is performed based on the crank sensor signal that is output each time the crank makes one rotation, the fuel injection during startup is not performed based on the engine stroke which results in excessive fuel being injected.
Although the technique disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-162691 performs an initial fuel injection determination in a batteryless system, there is no correlation between the generator output voltage and the engine stroke. There is a possibility that excessive fuel will be injected during an operation to detect the startup commencement crank angle or during a low-speed startup operation (for example, in the case of a miskick).
Moreover, when a determination voltage threshold value for an initial fuel injection is set on the high voltage side in order to prevent an excessive fuel injection, fuel injection is not performed at the required timing, and startability deteriorates.
In the technique disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-162543, when it is detected that the crank angle is at top dead center, it is necessary to determine that this top dead center is the intake top dead center. In engines that are only able to be cranked approximately three revolutions in a single startup operation, it is not possible to determine whether or not the stroke is the intake stroke at the top dead center. Moreover, there is a possibility that fuel will not be injected at the necessary timing because the determination is made after the compression top dead center at 360° to the rear has been exceeded due to the top dead center crank angle speed. As a result, it is not possible to ensure startability.